A post and core is a dental restoration used to sufficiently build-up tooth structure for future restoration with a crown when there is not enough tooth structure to properly retain the crown due to loss of tooth structure to either decay or fracture. In many cases the dental root is removed leaving an empty root canal in the tooth. Typically a thin rigid post (e.g. metal post) is inserted into the root canal and this post provides retention for a “core” which is a build up of material that replaces the lost tooth structure. The post can be cemented within the root canal and the core, which is an artificial preparation provides retention for the crown or coping replacing the tooth. The term “post and core” is also referred to as “post-and-core” and “inlay core”. Post and core restorations are often characterized as “foundation restorations”.
In a root canal procedure the nerve of the tooth is typically removed by the dentist using a dental drill, a so called endodontic procedure, leaving a bore in the tooth. In many cases a special post can be provided that matches the shape of the drill and after drilling the post can be directly cemented in the bore. However, the tooth root canal may have a non-regular structure and the bore in the tooth after removing the root is often also irregular, but even for the regular shapes the depth of the bore may be unknown. No post can thereby match the bore and a custom post must be provided.
A typical procedure when designing a post and core is that the dentist provides an impression of the prepared tooth with the bore and possibly also adjacent teeth and sends it typically to a dental technician at a dental laboratory. From this impression a dental model, such as a gypsum model, can be poured, and the dental restoration including the post and core can now be build from the dental model. The dental technician typically builds the post and core in wax, and then performs an investment casting, such that the real post and core is manufactured in a suitable material, e.g. a metal alloy.
WO10097089A discloses a computer-implemented method of designing and/or manufacturing a post and core to match a bore of a tooth, said method comprising the steps of: a) obtaining at least one impression of a set of teeth comprising a bore; b) scanning the impression of the set of teeth comprising the bore; c) providing a three-dimensional scan representation of the impression comprising the bore; d) transforming the three-dimensional scan representation to a three-dimensional positive working model of the set of teeth and the bore; and e) designing a post and core model from the positive working model of the bore.
Furthermore it is disclosed that when removing the tooth root/tooth nerve the dentist have used one or more dental drills. Thus, the shape of the resulting tooth bore is at least partly determined by the shape and/or type of the drill(s) processing the bore. In a further embodiment of the invention the post and core model and/or the post model is matched with the shape of the dental drill that created the bore. This is provided to improve the post and core model. Matching the shape can be merging and/or combining shape information of the dental drill(s) that created the bore, shape information such as a CAD model of the drill(s). Thereby scan artefacts of the post and core model can be identified and/or removed. E.g. a notch or cut in the post and core model can be identified as a scan artefact by knowing that use of the particular drill used could not have provided such a notch or cut.
It remains a problem to provide an alternative method for virtually designing a post and core restoration.